Auditory abnormalities in autistic children

Central Auditory and Vestibular Dysfunction Are Key Features of Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by repetitive behaviors, poor social skills, and difficulties with communication. Beyond these core signs and symptoms, the majority of subjects with ASD have some degree of auditory and vestibular dysfunction. Dysfunction in these sensory modalities is significant as normal cognitive development depends on an accurate representation of our environment. The hearing difficulties in ASD range from deafness to hypersensitivity and subjects with ASD have abnormal sound-evoked brainstem reflexes and brainstem auditory evoked potentials. Vestibular dysfunction in ASD includes postural instability, gait dysfunction, and impaired gaze. Untreated vestibular dysfunction in children can lead to delayed milestones such as sitting and walking and poor motor coordination later in life. Histopathological studies have revealed that subjects with ASD have significantly fewer neurons in the auditory hindbrain and surviving neurons are smaller and dysmorphic. These findings are consistent with auditory dysfunction. Further, the cerebellum was one of the first brain structures implicated in ASD and studies have revealed loss of Purkinje cells and the presence of ectopic neurons. Together, these studies suggest that normal auditory and vestibular function play major roles in the development of language and social abilities, and dysfunction in these systems may contribute to the core symptoms of ASD. Further, auditory and vestibular dysfunction in children may be overlooked or attributed to other neurodevelopmental disorders. Herein we review the literature on auditory and vestibular dysfunction in ASD. Based on these results we developed a brainstem model of central auditory and vestibular dysfunction in ASD and propose that simple, non-invasive but quantitative testing of hearing and vestibular function be added to newborn screening protocols.

Structural and Functional Aberrations of the Auditory Brainstem in Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a neurodevelopmental condition associated with difficulties in the social, communicative, and behavioral domains. Most cases of ASD arise from an unknown etiologic process, but there are numerous risk factors, including comorbidities and maternal exposures. Although it is not part of the diagnostic criteria, hearing difficulties ranging from deafness to hyperacusis are present in the majority of persons with ASD. High-functioning children with ASD have been found to have significantly slower and asymmetric auditory brainstem reflexes. Additionally, histopathological studies of postmortem brainstems in decedents who had ASD have consistently revealed significantly fewer neurons in auditory nuclei compared with those in people who did not have ASD. The authors review the literature implicating auditory dysfunction in ASD along with results from human study participants and postmortem human brain tissue. Together, these results implicate significant structural and functional abnormalities in the auditory brainstem in ASD and support the utility of auditory testing to screen for ASD.

Audiometric Profiles in Autism Spectrum Disorders: Does Subclinical Hearing Loss Impact Communication?

Rates of hearing impairment in individuals with Autism Spectrum Disorders (ASD) are higher than those reported in the general population. Although ASD is not caused by hearing impairment, it may exacerbate symptomatology. Participants with ASD (N = 60) and typically developing peers (N = 16) aged 5-18 years underwent a comprehensive audiological screening (pure tone audiometry, uncomfortable loudness level, tympanometry, acoustic reflexes, distortion product otoacoustic emissions, and auditory brainstem response) and assessment of communication abilities (expressive/receptive language, articulation, phonological awareness, and vocal affect recognition). Incidence of abnormal findings on at least one measure of audiological functioning was higher for the ASD group (55%) than controls (14.9%) or the general population estimate (6%). The presence of sound sensitivity was also considerably higher for the ASD group (37%) compared with controls (0%) or general population estimates (8-15%). When participants with ASD were dichotomized into groups with and without evidence of clinical audiological abnormality, no significant differences were identified on measures of communication; however, results of correlational analyses indicated that variability in hearing thresholds at middle range frequencies (2000 Hz) was significantly related to performance on all measures of speech articulation and language after correction for multiple comparisons (r = -0.48 to r = -0.53, P <  0.0045). These findings suggest that dichotomized classification of clinical audiology may not be sufficient to understand the role of subclinical hearing loss in ASD symptomatology and that treatment studies for mild/subclinical hearing loss in this population may be worthwhile.

Reducing auditory hypersensitivities in autistic spectrum disorder: preliminary findings evaluating the listening project protocol

Auditory hypersensitivities are a common feature of autism spectrum disorder (ASD). In the present study, the effectiveness of a novel intervention, the listening project protocol (LPP), was evaluated in two trials conducted with children diagnosed with ASD. LPP was developed to reduce auditory hypersensitivities. LPP is based on a theoretical "neural exercise" model that uses computer altered acoustic stimulation to recruit the neural regulation of middle ear muscles. Features of the intervention stimuli were informed by basic research in speech and hearing sciences that has identified the specific acoustic frequencies necessary to understand speech, which must pass through middle ear structures before being processed by other components of the auditory system. LPP was hypothesized to reduce auditory hypersensitivities by increasing the neural tone to the middle ear muscles to functionally dampen competing sounds in frequencies lower than human speech. The trials demonstrated that LPP, when contrasted to control conditions, selectively reduced auditory hypersensitivities. These findings are consistent with the polyvagal theory, which emphasizes the role of the middle ear muscles in social communication.

Childhood vision impairment, hearing loss and co-occurring autism spectrum disorder

BACKGROUND

Limited population-based data on prevalence of childhood vision impairment (VI) and hearing loss (HL), and their co-occurrence with autism spectrum disorder (ASD) exists.

OBJECTIVE

To examine prevalence and characteristics of VI, HL and co-occurring ASD among 8-year-olds in metropolitan Atlanta 2000-2008.

METHODS

We used data from the population-based Metropolitan Atlanta Developmental Disabilities Surveillance Program. Prevalence, birth and parental characteristics, presence and severity of other co-occurring developmental disabilities, and age of earliest identification of ASD, were examined for children with VI and HL, by co-occurring ASD.

RESULTS

VI and HL prevalences were 1.2 and 1.3 per 1000 8-year-olds, respectively. Approximately 6-7% of children with VI or HL had co-occurring ASD. Children with VI or HL with co-occurring ASD differed from those without co-occurring ASD by select birth characteristics and the presence of other co-occurring DDs. The median age of earliest known ASD diagnosis was significantly later among children with VI and ASD compared to children with ASD without VI (79 vs. 56 months). Children with HL and ASD were first evaluated by a community provider significantly earlier than those with ASD without HL (40 vs. 50 months).

CONCLUSIONS

The frequency of co-occurring ASD with VI and HL is higher than the population prevalence of ASD. The significant delays in diagnosis of ASD in children with VI and lack of earlier diagnosis of ASD among children with HL despite earlier evaluation highlight the importance of developing screening tools for early identification of ASD among children with VI and HL.

Respiratory sinus arrhythmia and auditory processing in autism: modifiable deficits of an integrated social engagement system?

The current study evaluated processes underlying two common symptoms (i.e., state regulation problems and deficits in auditory processing) associated with a diagnosis of autism spectrum disorders. Although these symptoms have been treated in the literature as unrelated, when informed by the Polyvagal Theory, these symptoms may be viewed as the predictable consequences of depressed neural regulation of an integrated social engagement system, in which there is down regulation of neural influences to the heart (i.e., via the vagus) and to the middle ear muscles (i.e., via the facial and trigeminal cranial nerves). Respiratory sinus arrhythmia (RSA) and heart period were monitored to evaluate state regulation during a baseline and two auditory processing tasks (i.e., the SCAN tests for Filtered Words and Competing Words), which were used to evaluate auditory processing performance. Children with a diagnosis of autism spectrum disorders (ASD) were contrasted with aged matched typically developing children. The current study identified three features that distinguished the ASD group from a group of typically developing children: 1) baseline RSA, 2) direction of RSA reactivity, and 3) auditory processing performance. In the ASD group, the pattern of change in RSA during the attention demanding SCAN tests moderated the relation between performance on the Competing Words test and IQ. In addition, in a subset of ASD participants, auditory processing performance improved and RSA increased following an intervention designed to improve auditory processing.

The contribution of muscular and auditory pathologies to the symptomatology of autism

Most research concerning the pathology of autism is focused on the search for central abnormalities that account for the production of symptoms. We, however, instead of looking at muscular and auditory features as merely associated manifestations, propose that they are somatic contributors by which some of the main clinical features of autism might be explained. Evidence suggests that muscles affect emotional experience. We think certain muscular dysfunctioning can impair communication and social interaction, and create stereotypic behavior, giving rise to the diagnostic features of autism. Furthermore, because speech is synchronized with facial movements and voice is controlled mainly through auditory feedback, a distortion of auditory feedback could disrupt voice, which in turn might cause parallel abnormal facial muscle functioning.

Cortical auditory processing and communication in children with autism: electrophysiological/behavioral relations

The purpose of the present study was to investigate the relations between late auditory evoked potentials (AEPs) recorded at temporal sites (the N1c wave or Tb) and verbal and non-verbal abilities in children with autism. The study was performed in 26 mentally retarded children with autism (AUT) aged 4-8 years (mean age +/- S.E.M. = 71 +/- 2 months; mean verbal and non-verbal developmental quotient +/- S.E.M. = 36 +/- 4 and 48 +/- 3). The stimuli used were 750 Hz tone bursts of 200 ms duration delivered binaurally at different intensity levels (50, 60, 70, 80 dB SPL) with 3-5 s interstimulus intervals. Temporal AEPs were first compared to those of a group of 16 normal children (NOR) in the same age range (mean age +/- S.E.M. = 69 +/- 3 months). We then focused on the AUT group and considered relations between temporal AEPs and the severity of disorders of verbal and non-verbal communication assessed using a behavior rating scale. AEPs recorded on left and right temporal sites were of smaller amplitude in the AUT group than in the NOR group. Increasing intensity-related amplitude was observed on both sides in NOR and only on the right side in AUT. The lack of intensity effect on the left side resulted in a particular pattern of asymmetry at the highest level of intensity (80 dB SPL) with greater N1c amplitude on the right than on the left side (the reverse was found in the NOR group). Electro-clinical correlations indicated that the greater the amplitude of the right temporal N1c responses, the higher the verbal and non-verbal communication abilities. This suggests a developmental reorganization of left-right hemisphere functions in autism, with preferential activation of the right hemisphere for functions usually allocated to the left hemisphere, particularly those involving the secondary auditory areas situated on the lateral surface of the superior temporal gyrus where the N1c/Tb wave is generated.

Auditory associative cortex dysfunction in children with autism: evidence from late auditory evoked potentials (N1 wave-T complex)

OBJECTIVES

Auditory processing at the cortical level was investigated with late auditory evoked potentials (N1 wave-T complex) in 4-8-year-old autistic children with mental retardation and compared to both age-matched normal and mentally retarded children (16 children in each group).

METHODS

Two negative peaks which occurred in the 80-200 ms latency range were analyzed according to stimulus intensity level (50 to 80 dB SPL): the first culminated at fronto-central sites (N1b) and the second at bitemporal sites (N1c, equivalent to Tb of the T complex). The latter wave was the most prominent and reliable response in normal children at this age.

RESULTS

Our results in autistic children indicated abnormalities of this wave with markedly smaller amplitude at bitemporal sites and pronounced peak latency delay (around 20 ms). Moreover, in both reference groups the intensity effect was found on both sides whereas in autistic children it was absent on the left side but present on the right.

CONCLUSION

These findings in autistic children showing very disturbed verbal communication argue for dysfunction in brain areas involved in N1c generation i.e., the auditory associative cortex in the lateral part of the superior temporal gyrus, with more specific left side defects when auditory stimulus have to be processed.

Autism and hearing loss

A group of 199 children and adolescents (153 boys, 46 girls) with autistic disorder was audiologically evaluated. Mild to moderate hearing loss was diagnosed in 7.9% and unilateral hearing loss in 1.6% of those who could be tested appropriately. Pronounced to profound bilateral hearing loss or deafness was diagnosed in 3.5% of all cases, representing a prevalence considerably above that in the general population and comparable to the prevalence found in populations with mental retardation. Hearing deficits in autism occurred at similar rates at all levels of intellectual functioning, so it does not appear that the covariation with intellectual impairment per se can account for all of the variance of hearing deficit in autism. Hyperacusis was common, affecting 18.0% of the autism group and 0% in an age-matched nonautism comparison group. In addition, the rate of serous otitis media (23.5%) and related conductive hearing loss (18.3%) appeared to be increased in autistic disorder. The study emphasizes the need for auditory evaluation of individuals with autism in order to refer those with pronounced to profound hearing loss for aural habilitation and to follow those with mild to moderate hearing loss because of the risk of deterioration.

Auditory Integration Training: The Magical Mystery Cure

Since its introduction in this country at the beginning of the decade, auditory integration training (AIT) has generated enthusiasm in parents and some clinicians, and harsh criticism by others. AIT has been promoted as a non-invasive treatment for auditory disorders that are believed to lead to attention and behavior problems. It has been particularly popular as a treatment for autism. Although parents cite numerous anecdotal reports of treatment success, many professionals frown on AIT's widespread practice prior to undergoing scientific scrutiny. The reasons for cautious evaluation of AIT prior to implementation in clinical practice are reviewed, along with a brief summary of current research findings.

The long-term effects of auditory training on children with autism

Eighty children, 3-17 years of age, with autism or Asperger syndrome and mild to severe distress in the presence of some sounds, were randomly allocated to two groups. The experimental group received auditory training and the control group listened to the same unmodified music under the same conditions. Significant improvements in behavior and severity of autism were maintained for 12 months by both groups. Informal data suggested that a range of abnormal responses to sound and other sensory abnormalities may also have improved. Verbal and performance IQ increased significantly 3 to 12 months after interventions. Findings suggest that some aspect of both auditory training and listening to selected unmodified music may have a beneficial effect on children with autism and sound sensitivity, and indicate a need for further research into the effects that led to these changes and the mechanisms involved in the sensory abnormalities commonly associated with autism.

Clinical use of otoacoustic emissions in children with autism

Transient-evoked otoacoustic emissions (TEOAEs) may offer an objective way of evaluating the peripheral auditory systems of difficult-to-test patients. Children with autism are often suspected of hearing loss, but frequently will not respond on traditional behavior auditory tests. The clinical feasibility of obtaining TEOAEs on children with autism was evaluated here. The use of TEOAEs for 6 children (12 ears) with autism is described here regarding the acquisition of data, the presence of emissions, and their amplitudes and reproducibility. Emissions were recorded for 9 of the 12 ears; the lack of emissions for the remaining 3 ears was due to lack of patient cooperation. The results suggest that TEOAEs may be a valuable part of the audiologic test battery for children with autistic behavior. The ease of obtaining emissions for these children with autism is discussed.

Auditory brainstem responses in autism: brainstem dysfunction or peripheral hearing loss?

The advent of electrophysiological techniques for audiologic and neurologic assessment in the late 60s has generated at least 11 auditory brainstem response (ABR) studies in autism designed to test the integrity of the auditory brainstem pathways. The results reported are contradictory, involving prolongation, shortening, and no abnormalities in central transmission latencies. When sample and methodological factors influencing the ABR are taken into consideration in the interpretation of results, the ABR data available at present can be seen as only suggestive, rather than supportive, of brainstem involvement in autism. Paradoxically, these studies revealed the presence of peripheral hearing impairment in a non-negligible number of autistic individuals. Additional evidence of auditory abnormalities as well as the implications for the clinician are considered.

Hearing-impaired autistic children

The charts of 46 children diagnosed as deaf and autistic were reviewed. Nearly one-fifth had normal or near-normal non-verbal intelligence and only one-fifth had severe mental deficiency. The severity of the autistic behavior was related to the severity of the mental deficiency, but not to that of the hearing loss. In 11 of the 46 children, autism went unrecognized for over four years after the diagnosis of hearing loss, and in 10 the hearing loss went unrecognized for several years after the diagnosis of autism. The educational experience of some children was generally disastrous because of the frequently late and incorrect diagnoses and the lack of specialized facilities for hearing-impaired autistic children.

Conductive hearing loss in autistic, learning-disabled, and normal children

Katz (1978) has suggested that mild, fluctuating conductive hearing loss due to middle-ear anomalies may account for the language and attention problems of learning-disabled children. His position was extended here to include autism. Normal, learning-disabled, and autistic children received repeated impedance measures over 5 weeks. A repeated-measures ANOVA of central tendency and variability values led to the conclusions that (1) fluctuating, negative middle-ear pressure greater than normal characterizes both autistic and learning-disabled children, (2) the negative pressure is greater in autistic than in learning-disabled children, and (3) the condition is typically bilateral for autistic children.